Fix convert_file for Python 3.13

[cjwatson]

As of python/cpython#117589 (at least), Path.glob returns an Iterator rather than Generator (which inherits from Iterator). convert_file doesn't need to care about this distinction; it can reasonably accept both.

This previously caused a test failure along these lines:

______________________________________________________ TestPypandoc.test_basic_conversion_from_file_pattern_pathlib_glob _______________________________________________________

self = <tests.TestPypandoc testMethod=test_basic_conversion_from_file_pattern_pathlib_glob>

    def test_basic_conversion_from_file_pattern_pathlib_glob(self):
        received_from_str_filename_input = pypandoc.convert_file("./*.md", 'html').lower()
>       received_from_path_filename_input = pypandoc.convert_file(Path(".").glob("*.md"), 'html').lower()

tests.py:654:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

source_file = <map object at 0x7f83952c9420>, to = 'html', format = None, extra_args = (), encoding = 'utf-8', outputfile = None, filters = None, verify_format = True
sandbox = False, cworkdir = '/home/cjwatson/src/python/pypandoc', sort_files = True
[...]
        if not _identify_path(discovered_source_files):
>           raise RuntimeError("source_file is not a valid path")
E           RuntimeError: source_file is not a valid path

pypandoc/__init__.py:201: RuntimeError

[JessicaTegner]

hey @cjwatson

It seems some CI is failing. Could you take a look at this

[cjwatson]

One of your indirect dependencies seems to have dropped PyPy 3.8 support. What do you want to do about that? Judging from PyPy's release notes it seems as though they've dropped 3.8 support, so maybe the easiest way out would be to just drop PyPy 3.8 support here, but that's not a decision I feel I can take for you. If you don't want to do that then I guess it would require some version pinning on PyPy 3.8, which would probably be a moving target.

[JessicaTegner]

there we go @cjwatson
I updated the CI workflow, dropping support for python 3.7, 3.8 and pyp3.8 ( #387 )

If you are all done with the fix, this can be merged